Reduced tropical cyclone densities and ocean effects due to anthropogenic greenhouse warming

Abstract:

Tropical cyclones (TCs) are the most fatal and costliest weather disasters on our planet. It is therefore of utmost importance to understand how their tracks, intensity and associated rainfall patterns will change in response to greenhouse warming. Due to the adoption of lower ocean model resolutions, previous modeling studies on the TC response to greenhouse warming underestimated such oceanic feedbacks. To address the robustness of TC projections in the presence of mesoscale air-sea interactions and complex coastal topography, we conduct century-long present-day, CO₂ doubling and quadrupling experiments using the Community-Earth-System-Model with 1/4^o atmosphere and 1/10^o ocean resolution. In response to CO2 doubling and quadrupling, the model simulates a decreased TC track density by 7 % and 32 % over almost the entire tropical and subtropical region. Less favorable environmental conditions for TC genesis, in particular a reduction of relative humidity and anomalous downward motion, can be linked to an overall weakening of the rising branches of the summer hemispheric Hadley cells. Moreover, we find an upsurge in precipitation and intensity of landfalling events. The ultra-high-resolution simulations show that atmosphere-ocean scale interactions play an important role in the sensitivity of extreme weather events to greenhouse warming.